Please help my understanding of the normal operation of a urban power network 1

[Sparky1949]

To facilitate responses I will number my thoughts

1.Is it correct that when loads reach a certain level, additional power sources (natural gas turbines, boilers, oil, and coal plants) are brought online?

2.Not all of these additional power sources are located at the same geographically located plant?

3.Not all of the energy from these additional power sources enter a load area via the same power lines, substations, and switchgear?

4.The load on the area's normally used power transmission lines prior a distribution substation may decrease when additional power sources are brought online over other power distribution lines?

5.The shift in load may take some time (minutes to perhaps hours) to develop?

6.There are records of which power plants, transmission lines, substations, and switchgear were online and when?

7.There are also records of repairs to the network listing what was repaired and when?

Since you read this far, let me tell you why I'm asking this. I am an old light commercial and residential electrician who is now working for a consulting firm. One of our clients is seeing some interesting DC voltages in the earth around their plant. Normally the voltages are consistent. However, some days they begin to shift in polarity and amplitude in one direction. Over a period of hours the amplitude increases. Then the polarity shifts in the other direction in minutes, and the amplitude increases manifold. The voltages stay there for a period of a few to eight or more hours. Then they shift in polarity and amplitude back to where they started in a period of minutes, followed by a slow transition to nominal.
Naturally, I have the job of finding the source of the voltages. I have looked at (datalogging for days with permission) many possible sources in the area and have found only one that looks at all similar. However, since starting this phase (no pun intended) of the project, there have been zero events at the plant. The similar pattern is on the neutral of a street light circuit.
Thank you for reading.
And, thanks in advance for your theories as to the source.

I have attempted to attach a jpg file of a sample graph from the project.
Sample Graph

 

[waross]

Cathodic protection?
Surface oxidation of a copper clad ground rod somewhere?
A loose and corroded connection on a neutral circuit somwhere?
I have seen copper oxide corrosion on a connection to a motor on a commercial printing press to the extent that when the polarity was reversed, the motor would not run in reverse.
A badly corroded neutral connection may pass current in one direction or polarity but block the opposite polarity, forcing the neutral current to return via a ground path. This may give a DC voltage the is in proportion to the loading on a neutral conductor somewhere.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

Records exist, but may be entirely unavailable. But the AC power grid isn't going to be the source for DC. Are you anywhere near where any form of HVDC transmission exists? Geomagnetic currents? Is there DC powered transit in the vicinity (rail or trolley bus)? Cathodic protection systems are a great source of DC, but wouldn't change polarity.

 

[ScottyUK]

What reference electrode are you using? Is it possible that the mass of earth is staying at a constant potential and whatever you are using as a reference is shifting instead? The voltages are in the range where they could easily be electro-chemical in origin. Do you have any irrigation / process drain operations / rain / septic tanks emptying etc which coincide with the shifts in voltage?

 

[crshears]

Davidbeach's response resonates with me; imho, the pattern you're describing suggests GIC [geo-magnetically induced current]. I find the phenomenon fascinating, as well as a grid operating PITA in the fortunately rare instances when it occurs.

You may find it worth researching, then seeing if you can establish any correlation with existing data on solar flare intensity...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]